One way to tell that you’re at the edge of viability for actual living at this point, as opposed to simply passing through or enduring it until better conditions arise, is that Antarctic mountain slopes appear to be completely sterile and free of microbes:
We analyzed 204 ice-free soils collected from across a remote valley in the Transantarctic Mountains (84–85°S, 174–177°W) and were able to identify a potential limit of microbial habitability. While most of the soils we tested contained diverse microbial communities, with fungi being particularly ubiquitous, microbes could not be detected in many of the driest, higher elevation soils—results that were confirmed using cultivation-dependent, cultivation-independent, and metabolic assays. While we cannot confirm that this subset of soils is completely sterile and devoid of microbial life, our results suggest that microbial life is severely restricted in the coldest, driest, and saltiest Antarctic soils. Constant exposure to these conditions for thousands of years has limited microbial communities so that their presence and activity is below detectable limits using a variety of standard methods.
Presumably if you brought microbes there, they would be able to endure for a while (and given aerial dispersal, they must be arriving constantly). But apparently no meaningful form of sustainable life at the microbial scale or higher is possible. (Similar to bacteria, spores, or tardigrades being able to survive exposure to space, and thus hitchhike to other planets or cause panspermia—but can’t actually grow, reproduce, or even just sustain a constant population in space.) Air might be similar: not so much because of the horrible salts in air, as its general lack of moisture and, well, everything else too.
So air can be a great medium for dispersal (as it is for even larger organisms like spiders), and there’s evidence about bacteria manipulating weather for this purpose, but it’s no place to live for biological life as we know it.
(Which of course says little about mechanical life: they don’t necessarily need any water, they can engage in complex logistics to move around atoms that they need like piping feedstocks up into the sky, they can create structures which bacteria would be utterly unable to like kites supporting solar panels or mirrors, they can use it bacteria-style for covert dispersal and do heavy industry on the ground, etc. They aren’t selfish little replicators which must evolve tiny fitness-incrementing step by step from little blobs of self-bootstrapping organic goo solely to maximize reproductive fitness under constraints of heavy predation & defection, among other limitations.)
If you can secrete the right things, you can potentially cause rain/snow inside clouds. You can see why that might be useful to bacteria swept up into the air: the air may be a fine place to go temporarily, and to go somewhere, but like a balloon or airplane, you do want to come down safely at some point, usually somewhere else, and preferably before the passengers have begun to resort to cannibalism. So given that even bacteriophage viruses are capable of surprisingly sophisticated community-wide decisions about when to kill their bacteria hosts and find greener pastures, and that bacteria communities can do similar calculations about dispersal or biofilm formation, it would not be too surprising if bacteria in a cloud storm might be computing things like timers or counting the average rate of organic matter floating upwards, to decide when to ‘try to land’ by everyone secreting special ice-nucleating molecules in the hopes of triggering the storm that will deliver them safely to the foreign ground, rather than waiting passively for a random storm which might put them down too late or somewhere bad.
One way to tell that you’re at the edge of viability for actual living at this point, as opposed to simply passing through or enduring it until better conditions arise, is that Antarctic mountain slopes appear to be completely sterile and free of microbes:
Presumably if you brought microbes there, they would be able to endure for a while (and given aerial dispersal, they must be arriving constantly). But apparently no meaningful form of sustainable life at the microbial scale or higher is possible. (Similar to bacteria, spores, or tardigrades being able to survive exposure to space, and thus hitchhike to other planets or cause panspermia—but can’t actually grow, reproduce, or even just sustain a constant population in space.) Air might be similar: not so much because of the horrible salts in air, as its general lack of moisture and, well, everything else too.
So air can be a great medium for dispersal (as it is for even larger organisms like spiders), and there’s evidence about bacteria manipulating weather for this purpose, but it’s no place to live for biological life as we know it.
(Which of course says little about mechanical life: they don’t necessarily need any water, they can engage in complex logistics to move around atoms that they need like piping feedstocks up into the sky, they can create structures which bacteria would be utterly unable to like kites supporting solar panels or mirrors, they can use it bacteria-style for covert dispersal and do heavy industry on the ground, etc. They aren’t selfish little replicators which must evolve tiny fitness-incrementing step by step from little blobs of self-bootstrapping organic goo solely to maximize reproductive fitness under constraints of heavy predation & defection, among other limitations.)
Sorry, what?
Ice-nucleating bacteria: https://www.nature.com/articles/ismej2017124 https://www.sciencefocus.com/planet-earth/bacteria-controls-the-weather
If you can secrete the right things, you can potentially cause rain/snow inside clouds. You can see why that might be useful to bacteria swept up into the air: the air may be a fine place to go temporarily, and to go somewhere, but like a balloon or airplane, you do want to come down safely at some point, usually somewhere else, and preferably before the passengers have begun to resort to cannibalism. So given that even bacteriophage viruses are capable of surprisingly sophisticated community-wide decisions about when to kill their bacteria hosts and find greener pastures, and that bacteria communities can do similar calculations about dispersal or biofilm formation, it would not be too surprising if bacteria in a cloud storm might be computing things like timers or counting the average rate of organic matter floating upwards, to decide when to ‘try to land’ by everyone secreting special ice-nucleating molecules in the hopes of triggering the storm that will deliver them safely to the foreign ground, rather than waiting passively for a random storm which might put them down too late or somewhere bad.